Electronic structures and magnetic properties of Li and Mn codoped LiZnN systems were investigated by using the first-principles calculations. Mn-doped LiZnN systems preferred the antiferromagnetic states, while Mn/Li codoped LiZnN systems were ferromagnetic and more stable than the Mn-doped LiZnN systems. The magnetic moments mostly arose from Mn-3d states, which hybridized with N-2p and Li-2s states near the Fermi level. The ferromagnetic coupling was suggested to be attributed to the p-d hybridization by the Mn-N-Mn chain. The results indicated that nonstoichiometry of Li was very essential for the ferromagnetism of Li (Zn, Mn) N system.